clk: qcom: Use the saved current frequency for enable_safe_config

A clk_get_rate in the clk_enable path would result in a BUG from sleeping
context, as clk_get_rate would hold a mutex when we have already acquired a
spinlock in the clk_enable.

Change-Id: I7b32292710bbea3565cdc51c79916fddc60f8bba
Signed-off-by: Taniya Das <tdas@codeaurora.org>